Today's Message Index:
----------------------
1. 08:02 PM - Re: vexing comm problem (Paul McAllister)
2. 11:28 PM - KX-155 & transmit interlock (Jim S)
Message 1
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| Subject: | Re: vexing comm problem |
--> Avionics-List message posted by: "Paul McAllister" <paul.mcallister@qia.net>
Hi,
I had a problem with my Lightspeed Headsets in my Europa (fiberglass). I
called Lightspeed and they fitted a shielded battery box which fixed the
problem for me.
Paul
----- Original Message -----
From: <bakerocb@cox.net>
Subject: Avionics-List: vexing comm problem
> --> Avionics-List message posted by: <bakerocb@cox.net>
>
> 6/16/2004
>
> Hello Brian Lloyd, and Other Willing Experts, I have a vexing problem with
the VHF comm portion of my Garmin 430 installed in my KIS TR-1 that I'd like
some help with. Here is the fundamental problem scenario:
>
> 1) Start engine, talk to ground control (121.8) using Lightspeed headset,
pilot's push to talk button, and pilot's headset jacks. Everything works
normally so taxi out and make engine run up.
>
> 2) Engine run up complete, switch to tower (133.1), try to talk using same
arrangement as in 1). The result is a machine gun like sound when I key the
transmitter -- impossible to transmit coherently. (Rapid intermittent making
and breaking of ground contact for PTT?). Receiver works OK.
>
> 3) Put on copilot's headset (David Clark) which is plugged into copilot's
jacks, use copilot's push to talk button and transmit clearly to tower to
request and receive take off clearance.
>
> 4) On some rare occasions (tower is familiar with the problem) I get take
off clearance without going to step 2), I take off, switch to departure
control (120.82 or 124.65)and have clear communications both directions with
departure control using the equipment in 1).
>
> 5) Upon return to home field at the end of a flight where the equipment in
1) above has worked fine on other frequencies I switch to 133.1 and get the
machine gun effect again when I key the transmitter -- impossible to
transmit coherently. I can solve the problem by using step 3).
>
> Here is what has been tried in the way of trouble shooting or problem
solving.
>
> A) Switched headsets between pilot's and copilot's jacks -- problem
remains.
>
> B) Extensively worked over pilot's headset jacks to eliminate any
intermittent problems that might exist.
>
> C) Extensively worked over pilots PTT circuit (not button itself) to
ensure good continuity.
>
> The baffling thing seems to be that the only two common items that don't
go away or can not be changed are the frequency of 133.1 and the pilot's PTT
button. When ever these two are combined regardless of what ever else is
changed this machine gun transmit problem may, but not in every instance,
exist.
>
> VHF comm antenna is a Bob Archer antenna mounted inside the fuselage side
aft of the copilot's seat.
>
> Any thoughts? Thanks for your help.
>
>
> 'OC' Baker, Builder of KIS TR-1 #116 4/14/97 - 11/17/03
>
>
Message 2
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| Subject: | KX-155 & transmit interlock |
--> Avionics-List message posted by: Jim S <gjs55@yahoo.com>
I am installing dual KX-155's and find no pin identified as a 'transmit interlock'
in the schematics. Am I missing something? I do see pin 14 on the Garmin 430
schematic. Is this option available on the KX-155? Thanks.
Jim
No need to move antennas. You need to verify that the "transmit interlock"
wiring between #1 and #2 Nav/Coms was installed correctly. The purpose of
this wiring is to reduce receiver sensitivity when the other Com radio is
transmitting. Both the KX155 and the 430 have this wiring option.
Mike
----- Original Message -----
From: "Brian Lloyd" <brianl@lloyd.com>
Subject: Re: Avionics-List: Bendix King Service Bulletins.....
>
> David Lloyd wrote:
>
> > I have a specific interest with the KX 155 comm. I am trying to find
methods to quiet RFI or similar that causes my Garmin 430 to break squelch
every time the King is keyed.
>
> This sounds like an overload problem in the Garmin 430, not a problem in
the King. Many receivers are going to have a problem with a transmitter
so
close in the same band. You might consider putting one antenna on the belly
and one on the top of the aircraft to provide more RF isolation.
>
> --
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